JP2004023738A - Image processing apparatus and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To implement color correction process within a preset tolerance against a color image signal in order for color appearances in multiple color reproduction scopes with different geometries to be nearly same. <P>SOLUTION: A mapping evaluation reference storage 205 stores color conversion reference parameters for making color appearances of each reproduction image to be nearly same for each output color space with different color reproduction scopes. A mapping parameter generator 204 generates a color conversion algorithm and color conversion parameters based on the reference parameters and input/output color space information. A profile generator 203 provides an input signal with color conversion based on the color conversion algorithm and the color conversion parameters to generate a profile, an evaluator 208 evaluates the color conversion result, and a corrector 209 corrects the color conversion parameters within a predefined tolerance based on the evaluation result to regenerate a profile. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and method for creating a color conversion parameter for performing a color conversion process on a color image signal.
[0002]
[Prior art]
In a conventional image processing apparatus, a color correction process is performed on an input color image signal so that an optimal image signal is reproduced in an output device. Such color correction techniques include the characteristics of the input image and the post-correction, such as photographic tonal correction, which preferably outputs image images, and graphics color correction, which preferably outputs business documents such as text and graph images. Are classified into a plurality of types according to the image quality.
[0003]
Further, as described in JP-A-8-256275, the conventional color correction processing aims to map input color space information to color gamut information in a printer. Therefore, predetermined algorithms and color correction parameters are created for the color gamut (for each color gamut when mapping to a plurality of different color gamut), and based on these, the color gamut information of the input color space information is created. Gamut mapping processing for. If the color correction result is not satisfactory, the user manually adjusts various color correction items and then verifies the color correction result.
[0004]
Here, when an image is output to a plurality of output media in the same printer, the color gamut (printer gamut) of the printer differs depending on the output medium. Need to be fixed. In this case, based on the relationship between the input color space and each printer color gamut, appropriate color conversion parameters and color conversion algorithms are created, and color correction processing using these is performed, thereby obtaining the color reproduced by the printer. The taste can be aligned.
[0005]
[Problems to be solved by the invention]
Even in the color correction method corresponding to a plurality of color gamut as described above, if the color correction result is not good, fine adjustment of the color correction parameters and the like has to be performed manually. However, since there is no guideline for the amount of adjustment in such manual fine adjustment, there is a problem that as a result of performing manual adjustment for a specific parameter, color reproducibility for the other parameter is deteriorated. there were. As described above, when performing the fine adjustment manually, an enormous amount of work is required to obtain an optimum image as a whole, and it is difficult for a user who is not experienced in the adjustment work.
[0006]
The present invention has been made in order to solve the above-described problem, and a color image signal within a predetermined allowable range is set so that colors in a plurality of color reproduction ranges having different shapes are substantially the same. It is an object of the present invention to provide an image processing apparatus and method for performing a color correction process in the above.
[0007]
[Means for Solving the Problems]
As one means for solving the above problems and achieving the object, the image processing apparatus of the present invention has the following configuration.
[0008]
That is, based on color space information of an input color signal and an output color signal, a parameter generation means for generating a color conversion algorithm and a color conversion parameter for converting the input color signal into the output color signal, and the input color signal A color conversion unit that performs color conversion based on the color conversion algorithm and the color conversion parameter, an evaluation unit that evaluates the color conversion result obtained by the color conversion unit, and the color conversion parameter based on the evaluation result obtained by the evaluation unit. And correcting means within a predetermined allowable range.
[0009]
Further, there is provided a data holding means for holding in advance allowable range data indicating the predetermined allowable range, wherein the correcting means corrects the color correction parameter with reference to the allowable range data.
[0010]
For example, the allowable range data indicates a predetermined hue range.
[0011]
For example, the data holding unit further holds in advance predetermined color conversion reference data and a color conversion parameter creation algorithm based on the color conversion reference data, and the parameter generation unit refers to the color conversion reference data, A color conversion algorithm and a color conversion parameter are generated.
[0012]
For example, the color conversion reference data and the color conversion parameters include iso-hue line data in a predetermined color space and coordinates of intersections between the iso-hue line and the color space outline of the output color signal.
[0013]
For example, the data holding unit further holds predetermined evaluation item data in advance, and the evaluation unit evaluates a color conversion result of the color conversion unit for an evaluation item indicated by the evaluation item data. I do.
[0014]
For example, the data holding unit further holds in advance tolerance data for an evaluation item indicated by the evaluation item data, and the evaluation unit determines a color in the color conversion unit for the evaluation item indicated by the evaluation item data. It is characterized by evaluating how much the conversion result matches the tolerance indicated by the tolerance data.
[0015]
For example, the color conversion unit maps the color gamut of the input color signal to the color gamut of the output color signal based on the color conversion algorithm and the color conversion parameter, and creates a color conversion profile based on the mapping result. It is characterized by doing.
[0016]
For example, the data holding means holds the data for each arbitrary image quality of a reproduced image based on the output color signal.
[0017]
For example, the data holding means holds the data in accordance with a type of a color space of the output color signal.
[0018]
For example, the data holding means holds the data so that substantially the same color is reproduced for each color space of the output color signal.
[0019]
For example, the data holding means holds data obtained from an external device.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0021]
<First embodiment>
● System overview
FIG. 1 is a block diagram illustrating a schematic configuration of the image processing apparatus according to the present embodiment. Referring to FIG. 1, reference numeral 101 denotes a CPU, which stores information data and control programs stored in a ROM 102, an OS (Operating System), an application program (hereinafter, referred to as an application), a color matching processing module, a device driver, and the like. Various controls of the unit 104, the image processing unit 105, the monitor 106, the input device 107, and the output device 108 are performed.
[0022]
An input device 107 inputs color space information data for which an arbitrary profile is desired to be created to the image processing apparatus by an image reading device such as an image scanner including a CCD sensor or a colorimetric device. An output device 108 outputs a visible image by an ink jet printer, a thermal transfer printer, a dot printer, or the like. The RAM 103 is a work area for various control programs and data input from the operation unit 104, and a temporary save area. An operation unit 104 performs setting of the output device setting unit 107 and input of data. Reference numeral 105 denotes an image processing unit that performs image processing including setting of gradation point information in the present embodiment and profile creation by color gamut mapping processing using the set gradation point information. Reference numeral 106 denotes a monitor, which displays a processing result of the image processing unit 105, data input by the operation unit 104, and the like.
[0023]
FIG. 2 is a block diagram illustrating a detailed configuration of the image processing unit 105. The image processing unit 105 is characterized in that a profile used for mapping input information in an arbitrary input color space to an output color space is created based on the mapping reference data, and is further evaluated and corrected.
[0024]
The mapping / evaluation reference storage unit 205 includes, as a part of its function, a parameter and an algorithm for performing processing for giving a similar color tone to a color conversion result with respect to an input color signal even when the shape of a color reproduction range is different. Further, parameters and algorithms necessary for color correction processing for realizing desired image quality (hereinafter, these are collectively referred to as mapping / evaluation reference data) are stored. The mapping / evaluation criterion storage unit 205 can read and store mapping / evaluation criterion data that achieves desired image quality by being connected to an external configuration via the terminal 212. A configuration in which a plurality of mapping / evaluation reference data are stored in the mapping / evaluation reference storage unit 205 and are switched according to a user instruction via the terminal 212 to execute a color correction process desired by the user It may be.
[0025]
Information about the color gamut of the printer, which is an output device, is input from a terminal 211, and input color space information, which is information about the color gamut of an input device, is input from a terminal 210. Reference numeral 201 denotes an input color space information storage unit which stores input color space information input via the terminal 210. An output color space information storage unit 202 stores printer color gamut information input via a terminal 211.
[0026]
Reference numeral 204 denotes a mapping parameter creation unit which refers to the printer color gamut information and input color space information, and the mapping / evaluation reference data stored in the mapping / evaluation reference storage unit 205, and performs mapping processing in the profile creation unit 203. The necessary mapping parameters are calculated.
[0027]
The profile creation unit 203 converts the color gamut of the input color space to the printer color based on the input color space information, the printer color gamut information, and the mapping parameters so as to reproduce the desired gradation image quality for the input information. Map to the reproduction range. Hereinafter, this mapping result is referred to as a mapping color gamut.
[0028]
The profile creation unit 203 also includes a correspondence relationship between the input color gamut and the mapped color gamut, input color information (RGB data) representing a predetermined color on the input color space, and a printer output color representing a predetermined color on the printer. With reference to the information (CMYK data), a profile for conversion from input data to printer output element data is created. The created profile is written into the RAM 206.
[0029]
On the other hand, the RGB image data to be corrected is input to the interpolation unit 207 via the terminal 213. The interpolation unit 207 performs conversion from RGB image data information to output element data with reference to the profile stored in the RAM 206, and outputs the conversion result via a terminal 213.
[0030]
FIG. 3 shows a memory configuration of the mapping / evaluation reference storage unit 205, that is, an example of the stored mapping / evaluation reference data.
[0031]
In a memory area 301 shown in FIG. 3, for each color component of red (R), green (G), and blue (B) in an input color space, a W-Col-Bk linking white (W) and black (Bk) is stored. Is stored in the form of a hue H in the HVC color space when the predetermined sample point in is mapped to the printer color gamut.
[0032]
The memory area 302 stores information on the hue correction allowable area at the R, G, and B mapping points, and is referred to when the correction unit 209 corrects the profile.
[0033]
In the memory area 303, RGB values of four colors Ac to Dc in the input color space are set as hue evaluation items.
[0034]
The memory area 304 stores a program 1 as a mapping target hue design algorithm described later.
[0035]
The memory area 305 stores a program 2 which is a target / permissible area design algorithm, and the memory area 306 stores a program 3 and a program 4 which are evaluation algorithms. These programs are read by the evaluation unit 208. Thus, the evaluation processing in this embodiment is realized.
[0036]
In the memory area 307, for the hue evaluation items Ac to Dc referred to by the evaluation unit 208, respective target hue values by color reproduction and allowable ranges are set by the hue H in the HVC color space.
[0037]
The memory area 308 stores a program 5 as an algorithm for performing coordinate conversion between the HVC space and the Lab space.
[0038]
In the profile creation unit 203 of the present embodiment, as shown in FIG. 3, by performing mapping processing based on mapping / evaluation reference data in which data for parameter creation and mapping algorithms are stored, the shape of the color reproduction range is reduced. Even if they are different, it is possible to realize a color conversion process in which the color conversion results for the input color signal look uniform. Specifically, a color conversion profile is created or corrected by referring to the mapping points and mapping parameters created based on the mapping / evaluation reference data in the mapping parameter creation unit 204.
[0039]
Hereinafter, the process of setting mapping points and mapping parameters for creating a profile in the present embodiment will be described in detail.
[0040]
● Mapping point setting processing
The mapping parameter creation unit 204 reads the mapping target hue and the mapping target hue design algorithm (program 1) from the memory areas 301 and 304 of the mapping / evaluation reference storage unit 205, and uses different printers for the R, G, and B color components. In the color gamut, mapping points exhibiting similar colors are set.
[0041]
Hereinafter, a process of setting mapping points exhibiting similar colors in different printer color gamuts in the mapping parameter creation unit 204 will be described using a red (R) component as an example.
[0042]
FIG. 4 is a diagram showing a cross section at a certain lightness of two printer color gamuts 402 and 403 having different color reproduction ranges and shapes in an HVC color space which is a coordinate system showing a visually uniform color distribution. . In the HVC color space, chromaticity points on the iso-hue line 401 at a certain hue H are identified as the same color by human vision. Therefore, the intersections 404 and 405 of the equal hue line 401 and the printer gamut 402 and 403 have different reproduced chroma, but visually look the same color. Therefore, in the present embodiment, a color exhibiting the same color tone even in a different printer color gamut is acquired as a mapping point based on isohue line information in the HVC color space.
[0043]
As described above, the hue H of the mapping point on the printer color gamut is a hue value in the HVC space, which is a coordinate system indicating a visually uniform color distribution, and is a display coordinate of the printer color gamut. It is necessary to perform coordinate transformation (mapping processing) on a certain Lab space.
[0044]
In the present embodiment, an algorithm for performing coordinate conversion between the HVC space and the Lab space is stored in advance in the memory area 308 in the mapping / evaluation reference data shown in FIG. Therefore, when setting the mapping parameters based on the mapping / evaluation reference data, even when a special value such as a coordinate value in the HVC space is designated instead of a value in the Lab space used for normal mapping processing. In the mapping parameter creation unit 204, the above-mentioned color space conversion algorithm and conversion information are read from the mapping / evaluation reference data, and the color space conversion is executed.
[0045]
Hereinafter, the input color space information is referred to as an RGB color space, and the distribution of surface sample points in the RGB color space is shown in FIG. FIG. 5 shows a cut plane obtained by cutting the color reproduction range in the RGB color space by a plane passing through three points of white (W), red (R), and black (Bk). In the figure, the upper left point indicates a white point W (255, 255, 255), and the lower left point indicates a black point Bk (0, 0, 0). The vertical axis represents a gray axis that changes from (0, 0, 0) to (255, 255, 255) in (R, G, B) coordinates. Also, Ri (i = 1 to 11) represents a surface sample point on the red (R) plane, the index i is a number assigned to the sample point in descending order of lightness, and R6 is the primary color red. Corresponding to The green (G) plane, the blue (B) plane, the cyan (C) plane, the magenta (M) plane, and the yellow (Y) plane are indexed with respect to the sample points in the same manner as the red (R) plane described above. Give the number.
[0046]
FIG. 6 is a diagram in which a red (R) section in the input color gamut and an R section in the printer color gamut are overlapped. According to the figure, it can be seen that the shape of the R section is different between the input color gamut and the printer color gamut.
[0047]
In the profile creation unit 203 of the present embodiment, for the sample surface points R1 to R11 shown in FIG. 5, the mapping lightness for the printer color gamut shown in FIG. 6 is converted into R1 ′ to R11 ′ shown in FIG. Set the profile.
[0048]
● Mapping parameter setting processing
The mapping parameter creation unit 204 sets, as mapping parameters, isohue line data and coordinates of its intersection with the outline of the printer color gamut.
[0049]
Hereinafter, with reference to a flowchart illustrated in FIG. 8, a process of setting mapping parameters for realizing mapping according to the present embodiment will be described in detail.
[0050]
Specifically, based on the mapping lightness set for the surface sample points R1 'to R11' shown in FIG. 7, or in the HVC color space in which the hue for the surface sample point is defined in advance by the mapping / evaluation reference data. Based on the hue value, a mapping hue target area (equal hue line data) on the printer color gamut for the sample point is set. In FIG. 8, the description will be made assuming that the brightness of the mapping target at the surface sample points R1 to R11 is L1 to L11, respectively.
[0051]
First, in step S801, input color space information and output color space information are obtained. In step S802, a counter (division number counter) indicating a target brightness value of equal hue line data is set. In step S803, a mapping target brightness Ln is selected. I do.
[0052]
Then, in step S804, the target hue value of the color for which the sample point is specified is acquired for the lightness Ln to be mapped. Here, the target hue value is stored in advance in the memory area 301 shown in FIG. 3 as mapping / evaluation reference data for each color, and each is indicated by the hue H in the Munsell color space. Therefore, in step S804, the Munsell hue value Hr, which is the designated hue value of red (R), is read from the memory area 301 and obtained as the target hue value.
[0053]
For convenience, it is assumed that the mapping point of the surface sample point Ri moving on the W-R6-Bk gradation line on the surface of the input color space shown in FIG. 5 also has the same mapping hue. When the mapping hues for Ri are different from each other, in the mapping / evaluation reference data shown in FIG. 3, the hue that performs the optimal color reproduction at the brightness to be mapped is held for each index i as the mapping target hue for each color. This may be obtained as the target hue value.
[0054]
As described above, in the present embodiment, the Munsell color space is defined as the HVC space for obtaining the equal hue line for each lightness, and the information that associates the coordinate points of the Munsell color space with the Lab color space is mapped and evaluated. Since it is stored as the reference data, it is possible to set equal hue line data for each mapping lightness based on the target hue value Hr and the mapping lightness Ln. Therefore, in step S805, iso-hue line data for obtaining coordinate points that realize the target hue value from 0 to the outer saturation is set so as to cover the printer color gamut.
[0055]
Specifically, in the HVC color space, the target hue value Hr for the mapping lightness Ln to be set as the hue line is realized and the hue line data changing in the saturation direction is defined by a Lab-HVC conversion algorithm and the like. Based on the obtained HVC color space reference data (described later), it is obtained as an HVC color space coordinate value. Although the hue line data may be information of continuous coordinate points (line segments) or some discrete coordinate point information, the hue line data in the present embodiment is the latter. It is assumed to be a form. The obtained hue line data (HVC color space coordinate values) are converted into Lab data in step S810 described later, and stored in the memory in the mapping parameter creation unit 204.
[0056]
Here, FIG. 9 shows an example of the equal hue line data stored in the memory in the mapping parameter creation unit 204. In the figure, memory areas 2001, 2009, and 2010 are sets of Lab coordinate data each representing a hue line with a hue setting target brightness of L * = L1, L2, L11. The indices shown at the left end of the memory areas 2002 to 2008 are obtained by assigning numbers to the iso-hue lines in ascending order of saturation when obtaining the iso-hue lines, and a * b on the corresponding iso-hue lines. * Coordinate points are stored respectively.
[0057]
Next, in step S806, the printer hue line information and the hue line data obtained in step S805 are used to obtain a coordinate point that realizes the target hue Hr in the outline of the hue line in the hue setting target brightness Ln. , The intersection coordinates of the contour of the printer color reproduction area and the iso-hue line are calculated.
[0058]
Then, in step S807, the value of the division number counter indicating the brightness value to be set of the equal hue line data is decremented, and the counter value is checked in step S808. If the counter value is 0, that is, the coordinate points and the equi-hue line data that realize all the target hue values in the outline of the printer color gamut have been calculated for all the lightness values for the equi-hue line setting. Become. Therefore, in this case, the process proceeds to step S809, in which all the calculated coordinate points are stored in the memory in the mapping parameter creation unit 204, and in step S810, the same hue line data is similarly stored, and the mapping shown in FIG. The parameter setting processing ends.
[0059]
Here, FIG. 10 shows an example of the intersection coordinate data stored in the memory in the mapping parameter creation unit 204 in step S809. The memory stores, for each specified color, the coordinates of the intersection of the contour of the printer color gamut and the iso-hue line for each mapping lightness. The memory area 2101 shown in FIG. 10 stores the mapping point coordinates in the Lab space for each of the sample points R1 to R11 and the W and Bk points which are the RGB input data shown in FIG.
[0060]
On the other hand, if the value of the division number counter is not 0 in step S808, the process returns to step S803, and the same hue line data for the remaining lightness Ln for setting the same hue line, and the coordinates of the intersection with the same hue line in the outline of the printer color reproduction area. Is calculated.
[0061]
FIG. 11 shows an example of the mapping parameters (coordinates of the intersection of the iso-hue line and its outline with the printer color reproduction threshold) obtained by the above processing. In the figure, the vertical axis represents the lightness axis (L *), the plane coordinate axes are the orthogonal coordinate axes a * and b * in the Lab uniform color system, respectively, and the printer color reproduction range is indicated by a solid line. Further, the lightness L1 to Ln on the dotted line between W and Bk is the equal hue line setting target lightness in the above processing, and the dotted line represents the Munsell hue 5R in red (R) associated with the lightness L1 to Ln. Fig. 3 shows the reproduced hue line data for each lightness.
[0062]
In FIG. 11, the intersection of the outline of W-Red-Bk in the printer color gamut and the isohue line data indicated by the dotted line is indicated by a black circle (●), and the black circle indicates the W-Red-Bk. A cross-sectional view is shown by the outline and a region surrounded by the gray line of W-Bk. The row of black circles on the outline of W-Red-Bk from W to Bk is the actual intersection coordinates, which are obtained based on the HVC space that changes evenly in brightness, hue, and saturation with respect to human eyes. Chromaticity point. In contrast to the chromaticity point indicated by the black circle, the chromaticity point on the iso-hue line at the equal lightness indicated by the white circle (○) appears to have changed the saturation with respect to the same color to human eyes.
[0063]
In the profile creation unit 203 of the present embodiment, the sample surface points R1 to R11 shown in FIG. 5 are based on the intersection coordinate data and the iso-hue line data stored in the memory in the mapping parameter creation unit 204 as described above. Is set so as to realize the mapping to R1 'to R11' shown in FIG.
[0064]
● Color reproducibility evaluation processing
In the present embodiment, it is evaluated whether sufficient color reproducibility can be obtained for the profile set as described above. Hereinafter, the color reproducibility evaluation processing will be described in detail.
[0065]
In the present embodiment, the interpolation unit 207 shown in FIG. 2 performs a color conversion process based on the profile created by the profile creation unit 203 and stored in the RAM 206. The color conversion result is evaluated by the evaluation unit 208. The evaluation unit 208 sets a hue evaluation color for image quality evaluation from the mapping / evaluation reference storage unit 205, acquires a color reproduction value by a profile for the hue evaluation color, and evaluates its chromaticity point. . As the hue evaluation colors, as shown in the memory area 303 of FIG. 3, among the RGB input values in the input color space, the RGB values of four colors Ac to Dc are set.
[0066]
The evaluation unit 208 obtains the color conversion output results of the RGB values of the hue evaluation colors Ac to Dc in the interpolation unit 207 as Lab color space coordinate values with reference to the printer gamut information, and obtains the Lab color space coordinate values. Is evaluated.
[0067]
In the memory area 307 of the mapping / evaluation reference data shown in FIG. 3, the information of the target hue value (Ht) and the allowable range (H1, H2) of the hue evaluation colors Ac to Dc by color reproduction are stored in the HVC. It is set by the hue H in the color space.
[0068]
Here, FIG. 12 shows the relationship between the target hue value and the allowable range in the hue evaluation color. FIG. 12 shows an a * b * coordinate plane in the lightness of the color to be evaluated, 1101 denotes a constant hue line of the target hue H in the color to be evaluated, and 1102 and 1103 denote constant hue lines in the allowable range hue.
[0069]
In the figure, if 1107 (■) is the coordinate of the evaluation target color (hue evaluation color), the target color coordinate having the same brightness and the same saturation as the evaluation target color 1107 is 1104 (●). 1105 and 1106 (○) which also have the same brightness and the same saturation as the evaluation target color 1107 across the target color coordinates indicate the allowable range coordinates. Also, an area between the target color coordinates 1104 and the allowable area coordinates 1105 is an allowable area A, and an area between the target color coordinates 1104 and the allowable area coordinates 1106 is an allowable area B.
[0070]
The evaluation unit 208 reads the program 2 which is the target / allowable area design algorithm stored in the memory area 305 shown in FIG. 3, and the programs 3 and 4 which are the evaluation algorithms stored in the memory area 306. The evaluation process is performed by executing.
[0071]
FIG. 13 is a block diagram illustrating a detailed configuration of the evaluation unit 208.
[0072]
In the figure, reference numeral 1001 denotes an evaluation target color data storage unit, which is a color reproduction value obtained based on the profile created by the profile creation unit 203 for the hue evaluation colors Ac to Dc, The color attribute and the Lab color space coordinate value are stored.
[0073]
FIG. 14 shows an example of data stored in the evaluation target color data storage unit 1001. The evaluation target color data storage unit 1001 includes, for each index for storing a plurality of evaluation target colors, an area for storing color attribute information of the target color and an area for storing Lab color space coordinate values. I have. In FIG. 14, a memory area 1701 stores an index 1 to be evaluated, an Ac identifier for evaluating a color to be evaluated as a hue evaluation color Ac as color attribute information, and a Lab color space coordinate value of the color to be evaluated. . Similarly, evaluation target color data for the hue evaluation colors Bc to Dc is also stored in the memory areas 1702 to 1704.
[0074]
Returning to FIG. 13, the evaluation target color data conversion unit 1005 sets brightness information and saturation information in the HVC color space based on the Lab color space coordinate values of the evaluation target color stored in the evaluation target color data storage unit 1001. . The set brightness information and saturation information are stored in the evaluation target color / target / permissible coordinate data memory 1007 together with the Lab color space coordinate values of the evaluation target color.
[0075]
The HVC color space reference data memory 1002 stores HVC-Lab conversion information and its algorithm from the memory area 308 of the mapping / evaluation reference storage unit 205, and is used when converting HVC-Lab coordinate values in other processing units. Used as appropriate.
[0076]
The target hue data memory 1003 and the allowable hue data memory 1004 store the target hue value for the color attribute information of the evaluation color in the data format of the hue information of the HVC color space from the memory area 308 of the mapping / evaluation reference storage unit 205. Each of the allowable hue values is stored.
[0077]
In the present embodiment, Lab values of the hue evaluation colors Ac to Dc have the same lightness and the same saturation, and the Lab coordinate points in the hue H based on the respective target hue values and the permissible range are represented by HVC color space coordinates. It is calculated based on the conversion information between the coordinates and the Lab color space coordinates. The calculated target chromaticity points and Lab coordinate points, which are the allowable chromaticity points, are stored in the evaluation target color / target / permissible coordinate data memory 1007.
[0078]
FIG. 15 shows an example of data stored in the evaluation target color / target / permissible coordinate data memory 1007. The memory area 1801 shown in FIG. 18 stores Lab coordinate values (Lp, ap, bp) for the color to be evaluated, lightness information Vp and chroma information Cp in the calculated HVC color space, and a hue calculated from the Lab coordinate values. The corner value hp is stored. Here, the hue angle h in the Lab color space is obtained from the Lab coordinate value (L, a, b) by the following equation (1).
[0079]
h = tan ^-1 (A / b) (1)
The memory area 1802 stores the Lab coordinate values (Lt, at, bt) of the target color for the evaluation target color and the hue angle value ht calculated from the Lab coordinate values. The memory area 1803 stores Lab coordinate values (Lt1, at1, bt1) in one allowable range for the evaluation target color, and a hue angle value ht1 calculated from the Lab coordinate values. The memory area 1804 stores Lab coordinate values (Lt2, at2, bt2) in the other allowable range for the evaluation target color, and a hue angle value ht2 calculated from the Lab coordinate values.
[0080]
Hereinafter, the color reproducibility evaluation processing in the evaluation processing unit 1008 shown in FIG. 13 will be described in detail. FIG. 16 is a flowchart showing the color reproducibility evaluation processing in the evaluation processing unit 1008, that is, the processing for determining whether the color to be evaluated is inside or outside the allowable range.
[0081]
First, in step S1301, the hue angle hp of the evaluation target color is obtained from the evaluation target color / target / permissible coordinate data memory 1007.
[0082]
In steps S1302 to S1304, the hue angle ht in the evaluation target color, the hue angle ht1 in one allowable range A, and the hue angle ht2 in the other allowable range B are stored in the evaluation target color / target / permissible coordinate data memory 1007, respectively. To win.
[0083]
In step S1305, the hue angle ht of the evaluation target color is compared with the hue angle ht1 of the allowable range A or the hue angle ht2 of the allowable range B to determine the allowable range hue angle including the target hue angle ht. It is determined whether the color to be evaluated exists on the allowable range A or the allowable range B.
[0084]
If it is determined in step S1305 that the evaluation target color is within the allowable range A, then in step S1306, the allowable range evaluation of the evaluation target color (permissible range A evaluation) is performed based on the evaluation target color and the allowable range A. . On the other hand, when it is determined that the evaluation target color exists in the allowable range B, the allowable range evaluation of the evaluation target color (the allowable range B evaluation) is performed based on the evaluation target color and the allowable range B in step S1307. The details of the allowable range evaluation processing in steps S1306 and S1307 will be described later.
[0085]
When the allowable range evaluation processing is completed, in step S1308, the result of determination of the inside and outside of the allowable range using the selected allowable range and the evaluation value of the evaluation target color for the evaluation target color calculated by the allowable range evaluation processing are stored in an evaluation value storage memory. 1009.
[0086]
In step S1309, the user is notified by displaying on the monitor 106 the results of determination of the inside and outside of the allowable range for each evaluation target color and the evaluation value of the evaluation target color for the evaluation target color stored in the evaluation value storage memory 1009. .
[0087]
As described above, according to the color reproducibility evaluation processing shown in FIG. 16, an allowable inside / outside determination result is obtained based on allowable range information in the mapping / evaluation reference data.
[0088]
FIG. 17 is a flowchart showing the allowable range evaluation processing shown in steps S1306 and S1307 of FIG. 16 described above, that is, the processing for determining the allowable inside / outside for the evaluation target color and the processing for obtaining the evaluation value for the target color.
[0089]
Here, FIG. 18 shows the relationship between the selected allowable range, the evaluation target color, and the evaluation target color for evaluating the evaluation target color. In FIG. 18, a black circle (●) 1201 indicates an evaluation target color and has a hue angle ht. A white circle (○) 1203 indicates the selected allowable area coordinate and has a hue angle htn. A square (■) 1202 indicates a color to be evaluated, and has a hue angle hp. Reference numeral 1204 denotes a difference between the hue angle between the evaluation target color 1201 and the allowable area coordinates 1203, and reference numeral 1205 denotes a difference between the hue angle between the evaluation target color 1201 and the evaluation target color 1202.
[0090]
First, in steps S1401 to S1403 in FIG. 17, the evaluation target hue angle hp, the evaluation target hue angle ht, and the hue angle htn of the selected permissible range coordinates are obtained. Then, in step S1404, an evaluation value V for the evaluation target color for the evaluation target color is defined and calculated by the following equation (2).
[0091]
V = | (hp−ht) | / | (htn−ht) | (2)
That is, the evaluation value V represents the ratio of the hue angle difference 1205 between the evaluation target color 1201 and the evaluation target color 1202 shown in FIG. 18 to the hue angle difference 1204 between the evaluation target color 1201 and the allowable range coordinates 1203. This ratio indicates the degree to which the target color is recognized as having the same color tone, that is, how much the evaluation target color looks like the target color. As the evaluation value V approaches 0, it looks like a target color, and as it approaches 1, the degree of recognition as the color decreases. Furthermore, it is evaluated that the value exceeding 1 is not recognized as the target color. Therefore, in step S1405, it is determined whether or not the evaluation value V obtained in step S1404 exceeds 1, and if V is 1 or less, it is determined in step S1406 that the value is within the allowable range. If V is larger than 1, step S1407 is performed. Is determined to be out of the allowable range.
[0092]
As described above, the evaluation result in the evaluation processing unit 1008 is stored in the evaluation value storage memory 1009. FIG. 19 shows an example of data stored in the evaluation value storage memory 1009.
In FIG. 19, the memory area 1901 stores the color reproducibility evaluation result of the evaluation target color indicated by the index Ac. Similarly, the memory areas 1902, 1903, and 1904 store the color reproducibility evaluation results for the evaluation target colors of the indexes Bc, Cc, and Dc, respectively. As described above, the evaluation value storage memory 1009 stores the color reproducibility evaluation result of the evaluation target color in association with the index. In addition, as the evaluation result, the color attribute of the evaluation target color, the determination result of the inside and outside of the allowable range, the evaluation value, and the distance ΔE between the target color Lab coordinate and the evaluation target color Lab coordinate are stored.
[0093]
● Profile creation / modification processing
The correction unit 209 shown in FIG. 2 determines whether to correct the created profile based on the comprehensive evaluation value in the evaluation unit 208. Here, the comprehensive evaluation value is, for example, the sum of the evaluation values calculated for each evaluation target color by the evaluation unit 208. If the total evaluation value is equal to or larger than a predetermined threshold, it is determined that the profile is not appropriate. The threshold for making this determination can be set as appropriate in the system.
[0094]
Hereinafter, the profile creation and correction processing in the present embodiment will be described in detail with reference to the flowchart shown in FIG.
[0095]
First, in the mapping parameter creation unit 204, input gamut information and output gamut information are acquired in step S1501, and in step S1502, based on the parameters and algorithm for determining the mapping points stored in the mapping / evaluation reference storage unit 205, Create mapping points and mapping parameters.
[0096]
In step S1503, the profile creation unit 203 executes a mapping process based on the mapping points and the mapping parameters. In step S1504, a color conversion profile is created based on the mapping result.
[0097]
Then, the evaluation unit 208 obtains an evaluation value for the evaluation item set based on the mapping / evaluation reference data in step S1505 as described above.
[0098]
Next, the correction unit 209 determines whether to correct the profile based on the evaluation value in step S1506. The determination may be made according to the presence or absence of a profile correction instruction from the user. If it is determined that the profile is not to be modified, the color conversion profile created in step S1504 is determined as the output profile, and the process ends. On the other hand, if it is determined that the profile is to be modified, the process advances to step S1508, and the modifying unit 209 performs profile modification processing.
[0099]
FIG. 21 is a flowchart showing the profile correction processing in the correction unit 209 shown in step S1508. Steps S1601 to S1603 in FIG. 21 are processes in the evaluation unit 208, and the mapping process and the profile creation process in steps S1608 and S1609 are processes in the profile creation unit 203.
[0100]
First, in step S1601, target / permissible hue data of a hue evaluation color stored in the memory area 307 of the mapping / evaluation reference storage unit 205 is set in the evaluation unit 208. Then, as described above, the evaluation unit 208 acquires a color reproduction value for the hue evaluation color in step S1602, and acquires an evaluation value for the hue evaluation color in step S1603.
[0101]
Then, in step S1604, the correction unit 209 determines whether or not the evaluation values for all the evaluation items have been obtained. If the evaluation values have not been obtained, the process returns to step S1601 to repeat the above-described evaluation processing. On the other hand, if all evaluation values have been obtained, the process advances to step S1605 to obtain an overall evaluation value as a sum of the evaluation values.
[0102]
In step S1606, it is determined whether the profile needs to be modified based on the comprehensive evaluation value acquired in step S1605. If the profile needs to be corrected, mapping parameters for profile correction are set in step S1607. That is, the correction unit 209 refers to the hue correction allowable area at the R, G, and B mapping points set in the memory area 302 shown in FIG. 3 from the mapping / evaluation reference storage unit 205 via the mapping parameter creation unit 204. Then, the mapping points of R, G, and B are corrected within this allowable range. In step S1608, a mapping process using the corrected mapping point is performed, and in step S1609, a profile is created based on the mapping result.
[0103]
Thereafter, the process returns to step S1601 and repeats the above process, thereby obtaining an evaluation value for the correction profile created in step S1609.
[0104]
Then, in step S1606, if the profile with the best overall evaluation value or the allowable profile is created, the process proceeds to step S1610, where the created profile is output as the optimum profile, and the process ends.
[0105]
As described above, according to the present embodiment, the printer is evaluated by the color reproducibility evaluation processing based on the allowable range and evaluation items in the mapping / evaluation reference data stored in advance, and the profile correction processing based on the evaluation result. It is possible to provide a profile capable of obtaining an optimal image for the color reproduction range.
[0106]
In the present embodiment, a profile is created by setting various combinations of the respective mapping design values within the allowable range set by the correction unit 209, and the evaluation unit 208 calculates the evaluation value. Good ones may be determined as profile creation parameters.
[0107]
Further, the evaluation color used in the evaluation processing in the present embodiment is not limited to the hue value, but may be lightness and saturation.
[0108]
Further, when various combinations of the mapping hue values of R, G, and B are set within the allowable range set by the correction unit 209, as a correction processing parameter, a hue value interval that divides the value within the allowable range is used. The value may be set by the user via the operation unit 104. Thus, the color correction result can be verified with the color correction accuracy desired by the user.
[0109]
[Other embodiments]
The present invention can be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, etc.), but may be a device including one device (for example, a copying machine, a facsimile machine, etc.). May be applied.
[0110]
Further, an object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or an apparatus, and a computer (or CPU or MPU) of the system or apparatus to store the storage medium. Needless to say, this can also be achieved by reading out and executing the program code stored in the.
[0111]
In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.
[0112]
As a storage medium for supplying the program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, and the like can be used.
[0113]
When the computer executes the readout program code, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code. It goes without saying that a case where a part of the actual processing is performed and the function of the above-described embodiment is realized by the processing is also included.
[0114]
Further, after the program code read from the storage medium is written into a memory provided on a function expansion board inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. It goes without saying that a CPU or the like provided in the board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.
[0115]
【The invention's effect】
As described above, according to the present invention, the color reproducibility between images output using different color gamut is aligned at the visual level of the user, and the allowable range and evaluation item stored in the image design data are By using the evaluation processing and the correction processing, a profile for obtaining an optimum image for the printer color gamut can be automatically created.
[0116]
Therefore, it is possible to easily perform color correction processing within a predetermined allowable range on the color image signal using the profile so that the color tone in a plurality of color reproduction ranges having different shapes is substantially the same. it can.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image processing system according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a detailed configuration of an image processing unit.
FIG. 3 is a diagram illustrating an example of data stored in a mapping / evaluation reference storage unit.
FIG. 4 is a diagram illustrating a relationship between printer gamut in an HVC color space.
FIG. 5 is a diagram illustrating an example of input color space data.
FIG. 6 is a diagram illustrating a relationship between an input color space and a printer color gamut.
FIG. 7 is a diagram illustrating an example of a mapped brightness.
FIG. 8 is a flowchart showing a mapping parameter setting process.
FIG. 9 is a diagram illustrating an example of isohue line data as mapping parameters.
FIG. 10 is a diagram showing an example of intersection coordinate data as mapping parameters.
FIG. 11 is a diagram illustrating an example of set mapping parameters.
FIG. 12 is a diagram illustrating a relationship between a target hue value and an allowable range in a hue evaluation color.
FIG. 13 is a block diagram illustrating a detailed configuration of an evaluation unit.
FIG. 14 is a diagram illustrating an example of data stored in an evaluation target color data storage unit.
FIG. 15 is a diagram showing an example of data stored in an evaluation target color / target / permissible coordinate data memory.
FIG. 16 is a flowchart illustrating a color reproducibility evaluation process.
FIG. 17 is a flowchart illustrating an allowable range evaluation process.
FIG. 18 is a diagram showing a concept of an evaluation value based on an allowable range, an evaluation target color, and an evaluation target color.
FIG. 19 is a diagram showing an example of data stored in an evaluation value storage memory.
FIG. 20 is a flowchart illustrating a profile creation process.
FIG. 21 is a flowchart illustrating a profile correction process.
[Explanation of symbols]
101 CPU
102 ROM
103 RAM
104 Operation unit
105 Image processing unit
106 monitor
107 Input device
108 Output device
201 Input color space information storage unit
202 Output color space information storage unit
203 Profile creation unit
204 Mapping Parameter Creation Unit
205 Mapping / Evaluation Criteria Storage
206 RAM
207 interpolation unit
208 Evaluator
209 Correction unit
210, 211, 212, 213 terminals
1001 Evaluation target color data storage
1002 HVC color space reference data memory
1003 Target hue data memory
1004 Permissible hue data memory
1005 Evaluation target color data conversion unit
1006 Target / permissible coordinate setting unit
1007 Evaluation target color / target / permissible coordinate data memory
1008 Evaluation unit
1009 Evaluation value storage memory

Claims (15)

Parameter generation means for generating a color conversion algorithm and a color conversion parameter for converting the input color signal into the output color signal, based on color space information of the input color signal and the output color signal,
Color conversion means for performing color conversion on the input color signal based on the color conversion algorithm and color conversion parameters,
Evaluation means for evaluating the color conversion result by the color conversion means,
Correction means for correcting the color conversion parameter within a predetermined allowable range based on the evaluation result by the evaluation means,
An image processing apparatus comprising: Furthermore, it has data holding means for holding in advance allowable range data indicating the predetermined allowable range,
2. The image processing apparatus according to claim 1, wherein the correction unit corrects the color conversion parameter with reference to the allowable range data. The image processing apparatus according to claim 2, wherein the allowable range data indicates a predetermined hue range. The data holding unit further holds predetermined color conversion reference data and a color conversion parameter creation algorithm based on the color conversion reference data in advance,
The image processing apparatus according to claim 2, wherein the parameter generation unit generates the color conversion algorithm and the color conversion parameters with reference to the color conversion reference data. 5. The color conversion reference data and the color conversion parameter include iso-hue line data in a predetermined color space, and coordinates of an intersection between the iso-hue line and a color space outline of the output color signal. Image processing device. The data holding unit further holds predetermined evaluation item data in advance,
The image processing apparatus according to claim 4, wherein the evaluation unit evaluates a color conversion result of the color conversion unit for an evaluation item indicated by the evaluation item data. The data holding unit further holds in advance tolerance data for an evaluation item indicated by the evaluation item data,
The evaluation unit evaluates, for an evaluation item indicated by the evaluation item data, how much the color conversion result of the color conversion unit matches the tolerance indicated by the tolerance data. Item 7. The image processing device according to Item 6. The color conversion unit maps the color gamut of the input color signal to the color gamut of the output color signal based on the color conversion algorithm and the color conversion parameter, and creates a color conversion profile based on the mapping result. The image processing apparatus according to claim 1, wherein: 9. The image processing apparatus according to claim 2, wherein the data holding unit holds the data for each arbitrary image quality of a reproduced image based on the output color signal. 9. The image processing apparatus according to claim 2, wherein the data holding unit holds the data according to a type of a color space of the output color signal. 11. The image processing apparatus according to claim 10, wherein the data holding unit holds the data such that substantially the same color is reproduced for each color space of the output color signal. The image processing apparatus according to claim 9, wherein the data holding unit holds data obtained from an external device. A parameter generation step of generating a color conversion algorithm and a color conversion parameter for converting the input color signal into the output color signal based on the color space information of the input color signal and the output color signal;
A color conversion step of performing color conversion on the input color signal based on the color conversion algorithm and a color conversion parameter;
An evaluation step of evaluating a color conversion result by the color conversion step,
A correction step of correcting the color conversion parameter within a predetermined allowable range based on the evaluation result of the evaluation step,
An image processing method comprising: 13. A program that, when executed on a computer, causes the computer to operate as the image processing apparatus according to claim 1. A recording medium on which the program according to claim 14 is recorded.

Images